This work studies the interaction of ADH and prostaglandins on Na, K, Cl, Ca, P and urea movement in the terminal nephron. The methods used are microinjection of distal tubules in the rat kidney, in vitro perfusion of isolated cortical collecting tubules of the rabbit and in vitro perfusion of inner medullary collecting tubules of the rat. Development of the techniques for electron probe microanalysis of frozen hydrated kidney tissue will allow measurement of the ionic concentrations and water movement in any tubular structures (frozen tubular fluid or frozen vascular fluid and adjacent cells) at any level in the kidney. Special analytical techniques developed and used in these projects are electron probe microanalysis and microfluorometry of fluid samples in picoliter final volumes.